Ink jet printing systems apply ink to a substrate. The inks are typically dyes and pigments in a fluid. The substrate can be comprised of an material or object. Most typically, the substrate is a flexible sheet that can be a paper, polymer or a composite of either type of material. The surface of the substrate and the ink are formulated to optimize the ink lay down.
Ink drops can be applied to the substrate by modulated deflection of a stream of ink (continuous) or by selective ejection from a drop generator (drop-on-demand). The drop-on-demand (DOD) systems eject ink using either a thermal pulse delivered by a resistor or a mechanical deflection of a cavity wall by a piezoelectric actuator. Ejection of the droplet is synchronized to motion of the substrate by a controller, which selectively applies an electrical signal to each ejector to form an image.
U.S. Pat. No. 6,491,385 to Anagnostopoulos et al., issued Dec. 10, 2002, entitled “CMOS/MEMS integrated ink jet print head with elongated bore and method of forming same,” describes a continuous ink jet head and it's operation. A silicon substrate supports layers on the front surface having a pair of resistive elements. A bore through the silicon substrate is supplied for each nozzle. A fluid, which can be ink, is forcibly ejected through the bore and through a nozzle formed in the layers on the front surface. The resistors are modulated to break the stream of fluid into discrete droplets. Asymmetric heating of the resistors can selectively direct the droplets into different pathways. A gutter can be used to filter out select droplets, providing a stream of selectable droplets useful for printing. The modulated stream printing system requires significant additional apparatus to manage fluid flow.
Piezoelectric actuated heads use an electrically flexed membrane to pressurize a fluid-containing cavity. The membranes can be oriented in parallel or perpendicular to the ejection direction. U.S. Pat. No. 6,969,158 to Taira, issued Nov. 29, 2005, entitled “Ink-jet head,” describes a piezoelectric drop-on-demand ink jet head having the membrane perpendicular to the droplet ejection direction. A set of plates is stacked up and includes plate of piezoelectric which flexes a pressure chamber parallel to the direction of ink ejection. The membranes require a large amount of surface area, and multiple rows of ejectors are arrayed in depth across the head. Ejectors are arranged across the printing direction at a pitch of 50 dpi and are arrayed in the printing direction 12 ejectors deep on an angle theta to form a head having an effective pitch of 600 dpi. Such heads are complex, requiring multiple layers that must be bonded together to form passages to the nozzle.
U.S. Pat. No. 6,926,284 to Hirst, issued Aug. 9, 2005, entitled “Sealing arrangements,” discloses a drop-on-demand inkjet head permitting single-pass printing. A single pass print head comprises 12 linear array module assemblies that are attached to a common manifold/orifice plate assembly. Droplets are ejected from the orifice by twelve staggered linear array assemblies that support piezoelectric body assemblies to provide drop-on-demand ejection of ink through the orifice array. The piezoelectric system cannot pitch nozzles closely together; in the example, each swath module has a pitch of 50 dpi. The twelve array assemblies are necessary to provide 600 dpi resolution in a horizontally and vertically staggered fashion.
The orifice array on the plate can be a single two-dimensional array of orifices or a combination of orifices to form an array of nozzles. In the printing application, the orifices must be positioned such that the distance between orifices in adjacent line is at last an order of magnitude (more than ten times) the pitch between print lines. The assembly is quite complex, requiring many separate array assemblies to be attached to the orifice plate thorough the use of sub frames, stiffeners, clamp bar, washers and screws.
It would be advantageous to provide a staggered array in a unitary assembly with an integral orifice plate. It would be useful for the spacing between nozzles to be less than an order of magnitude deeper than is disclosed in this patent.
U.S. Pat. No. 6,722,759 to Torgerson et al., issued Apr. 20, 2004, entitled “Ink jet printhead,” describes a common thermal drop-on-demand inkjet head structure. The drop generator consists of ink chamber, an inlet to the ink chamber, a nozzle to direct the drop out of the cavity and a resistive element for creating an ink ejecting bubble. Linear arrays of drop generators are positioned on either side of a common ink feed slot. Two linear arrays are fed by a common ink feed slot. Ink from the slot passes through a flow restricting ink channels to the ink chamber. A heater resistor at the bottom of the ink chamber is energized to form a bubble in the chamber and eject a drop of ink through a nozzle in the top of the chamber. The ejectors are constrained to be in linear rows on either side of the ink jet supply slot.
U.S. Pat. No. 6,367,903 to Gast et al., issued Apr. 9, 2002, entitled “Alignment of ink dots in an inkjet printer,” discloses a similar structure. The arrays of drop generators are not in a strictly linear fashion, but are slightly offset in groups of three and four generators. Generators in a group are displaced sequentially farther from the supply slot within a group. Adjacent nozzles between the groups have a maximum variation in distance from the common supply slot.
U.S. Pat. No. 5,134,425 to Yeung, issued Jul. 28, 1992, entitled “Ohmic heating matrix,” discloses a passive two-dimensional array of heater resistors. The structure and arrangement of the droplet generators is not disclosed. The patent discloses the problem of power cross talk between resistors in two dimensional arrays of heater resistors. Voltages firing a resistor also apply partial voltages across unfired resistors. The parasitic voltage increases as the number of rows is increased to 5 rows. The patent applies partial voltages on certain lines to reduce the voltage cross talk. The partial energy does not eject a droplet, but maintains a common elevated temperature for both fired and unfired nozzles. The patent covers print head arrays having limited numbers of rows.
U.S. Pat. No. 5,548,311 to Hine, issued Aug. 20, 1996, entitled “Mount for replaceable ink jet head,” discloses a piezoelectric drop-on-demand print head having a replaceable ink jet head. A set of nozzles selectively ejects ink when from electrical pulses are applied to transducers. The transducers are connected by wires to a series of spring contacts on the surface of the head that are electrically connected to a second set of contacts in a mobile carriage. The head structure uses connectors for each of 32 ink jets. The 32 contacts require 160 of clamping force to make a connection. A total of 400 grams of force needs to be applied at the connection to prevent disconnection due to g-forces when the carriage holding the head is translated during printing. It would be useful to reduce the complexity of the interconnection.
U.S. Pat. No. 4,791,440 to Eldridge et al., issued Dec. 13, 1988, entitled “Thermal drop-on-demand ink jet print head,” discloses a structure for a DOD thermal inkjet head. A heater chip, nozzle plate and chip mount are combined to produce a pluggable unit which has both fluid and electrical connections. The patent describes the increase in cost and complexity of electrical fanout and electrical connection as the supporting electrical connections as nozzle count increases. The patent addresses those issues by organizing the heating means in multiple column and passing electrical connection through the substrate. Through connections are more complex and costly. The device has no internal semiconductor elements, and a dedicated connection is required for each heater. The author organizes the heating elements in two staggered rows on either side of tow large holes supplying a common
As such, there is a need to provide a replaceable ink jet print head structure available at a reduced cost having a reduced number of semiconductor devices and electrical interconnections.